After a few unsuccessful attempts we finally obtained some good results. The next step was to go out and record some data. We found three adjacent music channels that fit within the 2.4MHz bandwidth of our receiver, allowing us to digitize them all at the same time. For example, a channel transmitting noisy rock music will have a wider bandwidth on average than a talk show channel (although all channels must remain inside their allotted 200kHz-wide band). Since it is an analog transmission, the bandwidth of an FM radio channel depends on the content that is being transmitted. A radar’s range resolution is proportional to the bandwidth of the illuminating signal, so we looked for the local FM radio stations with the widest bandwidths.
We used FM radio broadcast as an illuminating signal since it has high transmit power and is available almost everywhere. Passive radars have even been implemented using signals from transmitters onboard satellites.
Additionally, WiFi and cellular LTE based passive radars have been developed to track targets at close range. VHF passive radar has also been used to study the upper atmosphere, allowing the detection of meteor trails and other ionospheric disturbances.
Max track doppler tv#
For example, systems using VHF or UHF band illumination such as FM radio or digital TV broadcast are commonly used to track airplanes. Passive radars come in many different varieties. By determining the frequency shift between the reference signal and the echo signal we can infer the target’s velocity. Additionally, the echo signal acquires a Doppler shift which is related to the speed of the target. By measuring this delay we can determine how far away the target is. Notice that the target echo seen by the observation channel is delayed with respect to the reference signal because of the extra distance it has travelled. An idealized version of this process is shown in the animation below. The second is the observation channel, which detects echoes of the illuminating signal that have bounced off radar radar targets. The first is called the reference channel, which directly receives the illuminating signal coming from the transmitter.
Instead, they take advantage of existing signals in the environment such as radio or TV broadcast.Ī simple passive radar system has two separate receiver channels. Passive radars are different from active radars in that they don’t have a transmitter of their own. These echoes can be analyzed to determine various properties of the targets, such as their location and velocity. Radio signals are emitted from the transmitter which then bounce off objects in the environment before being detected back at the receiver.
Max track doppler software#
The GitHub repo for the processing software is here.įirstly, what does it mean for a radar system to be passive? Conventional radar systems are ‘active’ – that is, they have a dedicated transmitter as well as a receiver. I’ll add links to later posts at the bottom of the page. In this initial post I’ll cover the basics of how passive radar works and go over some of our results.
Max track doppler series#
It turned out to be a super fun and challenging project, so I am writing a series of blog posts covering the design of our system in case others find them interesting. My friend Derek and I recently built a passive radar system as a university design project.
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